The present invention relates generally to crop harvesting process and, more particularly, to improvements in flexible headers having a cutterbar that is vertically movable relative to the frame of the header.
To harvest crops growing close to the ground, such as soybeans, it is necessary to get the cutterbar of the crop harvesting header as close to the ground as possible without permitting the cutterbar to impact into the ground. Floating cutterbars, such as depicted in U.S. Pat. No. 3,388,539 and U.S. Pat. No. 3,886,718, could be attached to a header to harvest crop close to the ground. Such add on cutterbars were able to flex vertically to follow minor irregularities in the shape of the ground surface, even though the header itself remained relative rigid and, thereby, cut crop material close to the ground along substantially the entire width of the header without great danger of damage due to impact with the ground.
To overcome disadvantages inherent in the floating cutterbars, such as properly feeding severed crop rearwardly toward the combine, the header itself has been designed to flex with the cutterbar along undulations in the ground surface, such as is seen in U.S. Pat. No. 3,982,383 and U.S. Pat. No. 4,091,602. Such prior art structures suffer from the disadvantage of not being able to vary the amount of counterbalancing force supplied to the cutterbar by the upwardly lifting spring members. Some prior art structures also have a problem of stabilizing the cutterbar from side-to-side movements due to momentum imparted to the cutterbar by the reciprocatory action of the cutterbar drive and to forces imposed by contact with the ground surface.